Scientists have long marveled at the complexity of biological systems. Although the presence of many components (genes, proteins, signaling molecules, cells) is an obvious way in which biological systems are complex, complexity also arises from the fact that biological components interact in interconnected, dynamic and, frequently non-linear ways. Whereas dealing with the first type of complexity often calls for the tools of statistics, database management, and automated analysis of large data sets, dealing with the second type of complexity calls more often for the tools of engineering, biophysics, and applied mathematics. A common interest in this second type of biological complexity has brought together an interdisciplinary group of 12 investigators at the University of California, Irvine, who are committed to working together to expand the scope of complex biological systems research on the campus. Many in the group have a common focus on transport and the interaction of transport processes with other cell- and tissue-level events. The group draws from departments in the schools of Biological Sciences, Medicine, Physical Sciences and Engineering, and possesses a synergistic combination of well-defined biological problems, state-of-the-art methods for detailed measurement of biological parameters, and first-class mathematical and computational capabilities for numerical solutions and simulations. This proposal seeks funding, in the form of a planning grant (P20), to support a three year period of expansion of research interactions and development of the necessary research, teaching and administrative infrastructure to become a Center of Excellence in Complex Biological Systems Research.